Generally, surface roughness measurement methods are classified into an optical method and a stylus method. To be specific, the optical method is classified into a light sectioning method and an interference method. The light sectioning method refers to a method of irradiating a slit beam to a surface of an object and measuring a surface roughness using light reflected therefrom. The interference method refers to a method of measuring a surface roughness by observing an interference pattern of light. Regarding the optical measurement method, conventionally, Korean Patent No. 10-0125442 discloses a method and apparatus for optical detection of a surface roughness by generating a light bead on a material surface and then detecting a surface roughness using light reflected therefrom.
Further, the stylus method refers to a method of measuring a surface roughness by bringing a diamond stylus into contact with a surface of an object and checking unevenness while moving the diamond stylus. Regarding the stylus measurement method, Korean Utility Model No. 20-0178075 discloses a portable surface roughness measuring apparatus which measures a roughness of a specimen with a stylus unit and compares the measured roughness with a roughness of a comparison specimen.
The optical measurement method has some problems of having low precision, difficulty in measurement while an object is moved at a predetermined speed or more, and a complicated structure. The stylus measurement method uses a diamond stylus, and, thus, has a risk of damage to a surface of an object. Further, the stylus measurement method has a problem of difficulty in measurement of a surface roughness if the object has a smooth surface.